Generally speaking, ‘mechanisms’ are mechanical devices that transfer or transform motion, force, or energy. For example, a reciprocating engine (e.g. in an automobile where the linear motion of a piston is converted to the rotational motion of a wheel) is a mechanism that converts linear motion into rotational motion. ‘Compliant mechanisms’ can be understood to be those mechanisms that achieve the transfer or transformation of motion, force, or energy via the elastic bending of their flexible members.
A relatively new class of materials that may be considered for the fabrication of compliant mechanisms are metallic glasses, also known as amorphous alloys. Metallic glasses are characterized by their disordered atomic-scale structure in spite of their metallic constituent elements—i.e. whereas conventional metallic materials typically possess a highly ordered atomic structure, metallic glass materials are characterized by their disordered atomic structure. Notably, metallic glasses typically possess a number of useful material properties that can allow them to be implemented as highly effective engineering materials. For example, metallic glasses are generally much harder than conventional metals, and are generally tougher than ceramic materials. They are also relatively corrosion resistant, and, unlike conventional glass, they can have good electrical conductivity. Importantly, the manufacture of metallic glass materials lends itself to relatively easy processing. In particular, the manufacture of a metallic glass can be compatible with an injection molding process.
Nonetheless, the manufacture of metallic glasses presents challenges that limit their viability as engineering materials. In particular, metallic glasses are typically formed by raising a metallic alloy above its melting temperature, and rapidly cooling the melt to solidify it in a way such that its crystallization is avoided, thereby forming the metallic glass. The first metallic glasses required extraordinary cooling rates, e.g. on the order of 106 K/s, and were thereby limited in the thickness with which they could be formed. Indeed, because of this limitation in thickness, metallic glasses were initially limited to applications that involved coatings. Since then, however, particular alloy compositions that are more resistant to crystallization have been developed, which can thereby form metallic glasses at much lower cooling rates, and can therefore be made to be much thicker (e.g. greater than 1 mm). These thicker metallic glasses are known as ‘bulk metallic glasses’ (“BMGs”).
In addition to the development of BMGs, ‘bulk metallic glass matrix composites’ (BMGMCs) have also been developed. BMGMCs are characterized in that they possess the amorphous structure of BMGs, but they also include crystalline phases of material within the matrix of amorphous structure. For example, the crystalline phases can exist in the form of dendrites. The crystalline phases can allow the material to have enhanced ductility, compared to where the material is entirely constituted of the amorphous structure.
Although metallic glasses and their composites can now be formed in dimensions that can allow them to be more useful, the current state of the art has yet to understand the properties of BMG-based materials (throughout the application, the term ‘BMG-based materials’ is meant to be inclusive of BMGs and BMGMCs, except where otherwise noted) to an extent where they can be used in the design, fabrication, and implementation of superior ‘macroscale’ compliant mechanisms, e.g. those where the operative/strained member has a thickness greater than 0.5 mm. Accordingly, there exists a need to have a fuller understanding of the material properties of BMG-based materials such that superior BMG-based macroscale compliant mechanisms can be efficiently designed, fabricated, and implemented.